Two-way communication system



Dec. 22, 1925- J. F. FARRINGTON TWO-WAY COMMUNICATION SYSTEM Filed D. 23, 1929 ,fm/enfer. L/a/l/y f.' Farr/hyfm by Patented Dec. 22.1925.

UNITED STATES means PATENT OFFICE.

JOHN

F. FARRINGTON, NEW YORK, N. Y., ASSIGNOR T0 WESTERN ELECTRIC COM- PANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

TWO-WAY COMM:UNICATIONk SYSTEM.

Application filed December 23, 1920. Serial No. 432,644.

To all whom t may concer/ni:

Be it known that I, JOHN F. FARRTNGTON, a citizen of UnitedStates, residing at New York, in the county of Bronx and State of `New York, have invented certain new and useful Improvements in Two-Tay Communication Systems, of which the following is a. full, clear, concise, and exact description.

This invention relates to a two-way signaling system, and more particularly to a two-way carrier wave signaling system. This application discloses matter first disclosed in an application of the saine inventor, Serial No. 326,986, filed September 27, 193.9, of which this application is accordingly a continuation in part.

Its object is broadly to provide to provide improved means for the simultaneous transmission and reception of signals by modulated carrier wave operation.

A. more specific object is to accomplish the purpose stated by conjugately relating the transmitting and receiving circuits in such a manner that the balance is effected between the signal frequency currents.

An additional object is to provide a twoway signaling system of the. above mentioned type in which the transmitting oscillator combines its function as such with that of a detector. Other objects will be-apparent from the following description.

ylhe means for carrying out the functions stated above preferably includes conjugat'ely related or balanced low frequency receivingv and transmitting circuits, the high frequency receiving and transmitting circuits not being so related.

In the specific embodiment to be described in some detail later and which is illustrative of one form of conjugate arrangement, the low frequency modulating current is impressed on the divided primary circuit of a transformer across the secondary of which may be connected a telephone receiver, the current from the llow frequency source flows through the one-half of the primary to the high frequency oscillator. The oscillator and low frequency source being related so as to constitute together a system of modulated high frequency wave generation commonly known as the constant current system of modulation. The usual high frequency choke coil is included in circuit with the oscillator to prevent the ow of high frequency current in the circuit of themedulating means. The low frequency current Hows also in the other half of the primary winding and through an artificial network adjusted to give a balance in the transformer secondary circuit with respect to the currents in the primaries. rll`he system enables the generation and transmission of a modulated carrier wave without interfering side tone current in the related receiver.

Although the carrier frequency current in the receiver circuit due to unbalance of the conjugate system with respect to carrier current frequencies, would not result in interference with the signaling frequency current, it would produce an undesirable heating effect in the circuit and, unless balanced, would also tend to cause variations vin the contents of the circuits and make dif-r ficult a stable condition of balance. Accordingly, means is-disclosed for balancing when necessary, the low frequency circuits at carrier frequency as well as at low frequency. An advantage in the use of a low frequency balance inheres in the greater facility with which the balance may be maintained.

The oscillator which constitutes an ele.- ment of the above described system and in which the modulation occurs, is capable of functioning also as a detector, constituting the system as described above, a two-way transmission system. Although it is recogniZed as broadly old to combine the functions of a modulator and detector in a single device, it is believed to be novel to utilize the transmitting and generating tube as a detector of a signal frequency current in a system for simultaneous two-way operation. The arrangement as described results in a simplicity of circuits and avoidance of expense incidental to the use of separate means for the two functions.

The invention will be more readily understood from a reading of the detailed description which follows, taken in connection with the accompanying drawing in which Fig. 1 shows one modified form of the system of the invention; Fig. 2 shows a system similar'to that of-Fig. l except as including Van alternative form of modulating and generating means; and Fig. 3 illustrates a modified form in which the two carrier frequencies may differ from each other. f

Referring specifically to Fig. l, the reference letters G, M, R and N designate respectively, an oscillator, modulator, receiver, and balancing network. rllhe oscillator O and modulator' M cooperate to generate a high frequency wave modulated in accordance with the low frequency signal impressed on the modulator input. The oscillator O is of a well known type working directly on the antenna l. The antenna is related to the circuits of the tube in a manner well known. The frequency generated is determined by the natural frequency of the antenna circuit i. e. by the capacity of the radiating member, the induetance of the coil 3 and the capacit-y of the condenser l. The adjustable connnection constituting the plate coupling between the antenna loading coil 3 and the plate circuit the generating tube provides a means for adviustment of the feed-back coupling without changing the frequency of the generated oscillations. A grid leak path including a capacity, a resistance and an inductance, the two first mentioned being in parallel with each other and in series with the inductance. is connected between the grid and filament of tube 2. Space current for the tube 2 is furnished by the source 5 through the speech frequency choke coil 6, one winding /l of the primary of transformer T, and high frequency choke coil 7. Shunted around the source 5 and coil 6 is the anode and cathode path of the vacuum tube 8. The inf ut circuit S) of the tube 8 is coupled to the i. icrophone circuit 10 which is representative of any suitable source of speech or other signaling frequency electrical waves er variations. The production of speech waves in the circuit l0 will cause a corresponding variation in the impedance of tube 8 which will in turn cause variation in the currents supplied to the tube 2. The choke coil (i keeps the urrent flow from the hatteii'y 5 substantially constant. The oscillator and the modulator hf cooperate to generate a modulated carrier wave according to a method commonly known as a choke control, constant current modulating system. The coil 7 substantially excludes the high frequency oscillations from the modulatimg` circuit including c( 'ls L, and L2.

rlhe artificial net-work N receives current from the modulating an'ipliiier through tl i. coil lig of the primary winding of the transformer T and is so ce gned that the currents circulating in coils Ll and L2 will have equal and opposite effects upon the secondary circuit of transformer T.

ln the system of F ig. l, the network N is of novel type by means of which there is cbtained a balance of currents in the ransformer primary due both to the low frei-uency variations of current in the output cf modulator tube 8 and high frequency oscillations derived from oscillator O. This insures a balance with respect to such high frequency current as may pass through choke coil 7. The circuits of the network have not only been made the exact duplicates of the oscillator' circuits in circuit with winding L1 so far as regards the impedance characteristics, but the tube 2 with its various connectionsis also duplicated. The network therefore functions as an actual oscillator whose oscillations are utilized to effect a balance of the high frequency currents from the oscillator t) which pass the choke coil 7. The designation dummy oscillator7 is applied to that form of balancing circuit which is capable of this function in addition to that of an impedance balance. The telephone receiver ll or other indicating means, may be connected directly across the secondary L3 of the trans-former but is here shown as induetively coupled with the output of an amplier A.. Accordingly, hy means of the circuit arrangements so far described, signals originating in circuit l0 may be transmitted to a distant communicating station as modulations of a high frequency current wave.y all without interference with the circuits R.

In receiving, the oscillator O combines its function as a generator of waves of carrier frequency with that of a detector by means of which a modulated carrier wave is resolved into components including one having the characteristics of the modulating wave at the distant station. This low fre'- queney wave may readily be transmitted through the high frequency choke coil 7. Arrows are shown adjacent the antenna to indicate its functions as a receiving and transmitting conductor f1 denoting the outgoing frequency and f2 the incoming. By reason of the oscillating characteristic of the detecting circuit, the well known self-amplifying effect is secured. The low frequency detected current flows through windings Ll and L2 and networrr N. This current is unbalanced with respect to the secondary L2 and therefore causes a response in receiver R. The network N and transformer T may be provided as a protection with grounded electrostatic shields in conformity with what has been found to be the best practice in that regard.

T he system of li 2 differs from that of F ig. l principally in the particular generating and transmitting means employed and the substitution for the dummy oscillator of l of an artificial network designed to produce a balance with respect to low frequencies'. lt is of well known type and comprises the necessary impedance elements to produce the desired balance. The systems of the two figures function in much the same manner and the two forms of networks shown, aS well as the specific generating and transmitting means, muy be used interchangeably. The network of Fig. l, however, has the additional function described above. nly so much of the system of Fig. 2 will be described below as is necessary to an understanding of the transmitting and generating circuits referred to.

I In particular cases it may be desirable to maintain a constancy of oscillation greater than can be secured by the means shown in Fig. 1, in which the oscillator oscillates directly into the antenna, and in which the modulating function occurs'in the oscillator. The means of Fig. 2 differs from that of Fig. 1 in that the oscillator oscillates into the input of the amplifier Al which in turn works into the antenna 1. The frequency of oscillation is determined by the constants of the circuit comprising an inductance 12 and the capacity of condensers 13 and 14. The remaining condensers shown function as stopping condensers for as grid condensers in accordance with a well known principle. Space current for the oscillator is provided directly by the battery 5 without the interposition of a lon7 frequency choke coil, the modulating function occurring on the amplifying tube A, which receives its space currentfrom source 5 through low frequency cho-ke 6 in the same manner as the oscillator receives current in Fig. l.

For a more detailed disclosure ofy a modulation system of this type, reference is made to U. S. Patent to Raymond A.i Heising 1,442,147, January 16, 1923, in which such a system is describedand claimed.

Fig. 3 illustrates a modified form of the system of Fig. 1, which provides means for applying the principle of the invention to the case where Vdifferent carrier frequencies are used for sending and receiving. Although in general, the arrangement of Fig. 1

combines the elements of simplicity, low

cost and utility to a maximum degree, it 1s evident that its effectiveness in a large part is dependent on the accuracy with which the two carrier frequencies may be maintained equal, inasmuch as, if the frequencies become slightly different, the detecting action of the tube 2 would result in a component of current having a difference frequency which would in the usual case be well within the audible range, and would cause, at the best,

an undersirable side tone in the receiver. The system of Fig. 3 avoids the necessity of a close correspondance of the carrier frequencies by permitting them to dier by an amount which will cause the difference frequency current to be inaudible and so not to interfere with the reception of the signals. The difference frequency component and the modulated difference frequency component may be suppressed, if desired, by the band filter FB which is adjusted to pass only the frequency signal component. In this figure the telephone receiver 11 is shown directly across the amplifier output although the corthe space current orv responding means shown in Fig. 1 may equally well be used. Also'aii artificial network of a conventional type has been substituted for the dummy oscillator of Fig. 1.

1n order to provide for the' case in which the antenna cannot be tuned broadly enough to send and receive effectively the currents of the two frequencies, the circuit'means shown at tlieleft of the antenna may be used. By meansof the circuit designated generally by 15 in shunt with elements 3 and 4, the'antenna is made resonant to the frequency of the received wave. v The resonant circuit 1G is'tuiied to the frequency of the transmitted wave and effectively excludes currents of this frequency from the. branch circuit. The arrangement results inv giving the antenna system two degrees of freedom.

The novel features which are believed to be vinherent in the invention are defined in the appended claims.

vWhat is claimed is:

1. A station vllor two-uf'ay communication systems comprising in combination a transmitting circuit and a receiving circuit,.including a transmitting and receiving conductor, common means for generating the outgoing high frequency carrier vwave and for detecting the incoming modulated carrier wave associated in energy transfer relation Awithsaid conductor, a modulating circuit associated with said means for modulating said high Vfrequency wave, a receiving device, and means conjugately relating portions of said transmitting and receiving circuits, whereby transmission-may be effected without interference with reception.

"2.151 station for two-way communication systems comprising in combination a transmitting and receiving conductor, a combined oscillating and detecting rmeans of the thermionic vacuum tube type associated therewith, including a space current source and coupled input and output circuits, a transformerv having a secondary, anda divided primary, winding, a low frequency choke coil, a `portion of said'divided transformer primary winding and the space current circuit of said means being in circuit with said space current source, a low frequency source in shunt with said low frequency choke coil, another portion of said divided primary winding beingk in circuit with said space current source and said choke coil, said portions being oppositely arranged with respect to the secondary winding, a receiving means in circuit with the secondary winding, and circuit means included in circuit with said second portion whereby the currents in said portions from said low'frequency source are balanced with respect to said secondary.

3. The system of claim 2 in which the said circuit means is an oscillator adapted to generate a wave similar in form and amplitude to that generated by said oscillating means.

means, a low frequency source in shunt Withsaid low frequency choke coil, another portion of said divided primary Windlngin circuit with said space current lsource and said cliolre coil, ,aid portions being oppositely arranged with respect to the secondary Winding, a receiving ineens connected across the secondary winding, and circuit `means inclnded in circuit with said second portion whereby the currents in said portions. are balanced with respect to said secondary.

yElie system of claim el in which said circuit means comprises an oscillation gcnerator.

6. A carrier Wave transmission system comprising a transmission circuit, means connected to said circuit in energy transfer' relation for generating, a high frequencycarrier Wave andy detecting an` incoming vmodulated' carrier Wave, a circuit for transmitting modulating currents to and detected` modulated current from saidmeans, amodulating source in energy transfer relation to said last mentioned circuit, a receiving device in energy transfer relation to said last men.-v

tioned circuit, and balancingv means for preventing the modulating current from affecting saidI receiving device.

7. A carrier Wave transmission system comprising in combination, a transmitting and receiving' conductor, common means aS- sociated Withsaid conductor for generating a high frequency carrier Wave andfor detecting the modulated carrier Wave received over saidconductor, a receiving device asso:

oated with said detecting ineens, modulat- Hg means associated nth Said concliwtpia and recel ing device, and means conyugately,

rent generating means, the Constants ofsaid.V

balen( net-Work bei so adjusted as to, @eine its impedance. and its generated-.oularent with respect to the common portion to be substantial duplicates of the impedance and generated current inthe individualiporltien ,of said fir-et mentioned circuit- 9'.. In a ,Carrier wir@ transmission System, a, transmitting ciri ft, common means connected in energy transfer relation-.to VSaid circuitvfor generating; a hiel froqiionoyout.- :iva-ve fand for, yd etecting a modulated Carrier incoming Wave, o modulatinssouroe and a receiving moans associ-ated', with Said common means and Circuits Cousine Said source and lieoevineimeens tobeconjusetely related, said circuits functioning as a balancing impedance which generates osollaf 10, In combination, av transmitting oscillator, means for controllingjsaidoscillator in accordance .with signals, 4a,ibalancing oscillator, said; oscillators being connected,tosaidV controlling means, and a receiving device electrically connected to oscillators in opposite senses Witlirespect to said controlling means, whereby outgoing ,signals fromL said controlling means are neutralized in their odset-on Said'rooeivor- In Witness` whereof, l hereunto subscribe my rnaine this 16th day 'of December D., 192.0..

Joint F. FARRlNGToN.

Til 

